The story of Lina and Kai follows their adventure in a post-apocalyptic world. After the failed experiment, Eon Nexus, the world took a radical turn. Among the survivors is Lina, the daughter of Alina, who is destined to bring peace and harmony to the world. Lina embarks on numerous adventures, encountering various individuals who either aid her or hunt her down.

At one point, Kai saves Lina during an attack, and they begin their journey together. Their mission is to find the Underground City, a place rumored to be untouched by the apocalypse or war, according to Lina's grandfather. Lina and Kai eventually discover the Underground City, a mysterious place hidden deep beneath the earth, marked by fragile beauty and growing tension.

At the center of the city stands a massive, glowing tree tied to Lina's past through a medallion inherited from her mother. They learn that Lina's mother is the essence of the tree, protecting the city at the cost of her own life. As they attempt to save the city, they are attacked by a horde of merciless seekers.

In a moment of despair, Lina and Kai confess their deep love for each other and transform into a giant being of light, defeating the attackers. Reaching the tree, Lina's mother reveals their ultimate destiny.